In recent years, an active matrix type liquid crystal display device that has advantages such as thin-profile, light-weight, low drive voltage, and low power consumption has been widely used as a display panel for various electronic devices such as mobile terminal devices including mobile phones, portable gaming devices, and the like or laptop computers.
A primary part of such an active matrix type liquid crystal display device includes a liquid crystal display panel as a display section that is constituted of a plurality of pixels that are arranged in a matrix, and a driver circuit therefor. In the liquid crystal display panel, a plurality of data signal lines (hereinafter referred to as “source bus lines”) and a plurality of scanning signal lines (hereinafter referred to as “gate bus lines”) are disposed so as to cross each other in a lattice pattern. Further, a plurality of auxiliary capacitance lines are disposed so as to extend in parallel with the plurality of gate bus lines. At each of the intersections of the plurality of source bus lines and the plurality of gate bus lines, one corresponding pixel is provided. The liquid crystal display panel also includes a common electrode (or an opposite electrode) that is commonly disposed for the plurality of pixels arranged in a matrix and that faces pixel electrodes provided in the respective pixels through a liquid crystal layer.
FIG. 11 is an equivalent circuit diagram showing an electrical configuration of two adjacent pixels in a liquid crystal display panel of a liquid crystal display device configured in a manner described above. Each pixel includes a thin film transistor (hereinafter abbreviated as “TFT”) 52 as a switching element and a pixel electrode 53 connected to the drain electrode of the TFT 52. The source electrode of the TFT 52 is connected to the source bus line 50 that passes through an intersection corresponding thereto, and the gate electrode is connected to the gate bus line 51 that passes through the same intersection. A liquid crystal capacitance C1c is formed by the pixel electrode 53 and the common electrode 54. An auxiliary capacitance Cs is formed by the pixel electrode 53 and the auxiliary capacitance line disposed along the gate bus line 51.
These liquid crystal capacitance C1c and auxiliary capacitance Cs form a pixel capacitance that holds a voltage that indicates a value of a pixel to be formed by each pixel. Also, in each pixel, a parasitic capacitance Cgd1 is formed between the pixel electrode 53 for the pixel and the gate bus line 51.
Because of the parasitic capacitance Cgd1 formed between the gate bus line 51 and the pixel electrode 53 in each pixel, when a data signal is applied to the source bus line 50, and when a voltage of a scanning signal is lowered from an ON voltage Vgh of the gate bus line 51 to an OFF voltage Vg1 of the gate bus line 51, a level shift ΔVd caused by the parasitic capacitance Cgd1 is generated in a potential (pixel potential) Vd of the pixel electrode 53. This level shift ΔVd is referred to as “feed-through voltage,” “lead-in voltage”, or the like. The feed-through voltage ΔVd is represented by the following formula:ΔVd=(Vgh−Vg1)·Cgd1/(C1c+Cs+Cgd1)  (1)
Such a feed-through voltage ΔVd causes flickering, quality degradation, and the like in a displayed image. Generally, in a liquid crystal display panel driven by TFTs, an asymmetric voltage applied to a liquid crystal layer causes flickering, thereby significantly lowering the display quality. It also causes image burn-in when left uncontrolled for a long period of time.
A liquid crystal display device for solving this problem has been proposed. Specifically, a liquid crystal display device that includes groups of wiring lines arranged in a matrix, a plurality of active elements, and a liquid crystal layer and that is configured such that conductive layers maintained at a prescribed potential are selectively disposed around pixel electrodes provided for the respective pixels has been disclosed. The disclosure describes that according to such a configuration, parasitic capacitances between the pixel electrodes and the gate bus lines can be reduced, and therefore, a swing of a voltage applied to the liquid crystal layer becomes smaller, resulting in the improvement of the picture quality (see Patent Document 1, for example).